CN108213404B

CN108213404B - Micro-powder and target type air flow milling powder preparation method for preparing neodymium iron boron permanent magnet material and powder discharge method

Info

Publication number: CN108213404B
Application number: CN201611189003.XA
Authority: CN
Inventors: 陈国安; 方彬; 孙立柏; 赵玉刚
Original assignee: Sanvac Beijing Magnetics Co ltd; Beijing Zhong Ke San Huan High Tech Co Ltd
Current assignee: Sanvac Beijing Magnetics Co ltd; Beijing Zhong Ke San Huan High Tech Co Ltd
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2022-01-28
Anticipated expiration: 2036-12-21
Also published as: US11571744B2; JP2020504782A; CN108213404A; WO2018113555A1; JP6963617B2; US20200030884A1

Abstract

The invention discloses micro powder for preparing a neodymium iron boron permanent magnet material, a target type airflow milling powder preparation method for preparing the micro powder and airflow milled powder. The sphericity of the micro powder is more than or equal to 90 percent, and the particle attachment rate is less than or equal to 10 percent; in the target type airflow milling powder method, the relationship among the diameter A of the target center, the diameter B of the side nozzle and the distance C between the target center and the side nozzle is as follows: and A/B is mx (C/A + B), wherein the value range of m is 1-7, the jet air velocity of the side nozzle is 320-580 m/s, and the relationship between the diameter F of the grading wheel and the diameter A of the target center is as follows: f is p multiplied by A, wherein the value range of p is 3-6; the airflow milled powder obtained by the method consists of superfine powder and the micro powder; wherein the proportion of the mass of the superfine powder to the total mass of the powder milled by the airflow is less than or equal to 0.5 percent. The micro powder in the invention has uniform particle size distribution, narrow range and low nitrogen content, is suitable for large-scale production of high-quality sintered neodymium-iron-boron permanent magnet materials, and the discharged powder obtained by the target type jet milling method does not contain spitting materials, thereby saving subsequent processes.

Description

Micro-powder and target type air flow milling powder preparation method for preparing neodymium iron boron permanent magnet material and powder discharge method

Technical Field

The invention relates to micro powder for preparing sintered neodymium iron boron permanent magnet materials, a target type airflow milling powder preparation method for preparing the micro powder, and airflow milled powder obtained by the method.

Background

With R₂T₁₄Sintered Nd-Fe-B multiphase material with B as main phaseThe material has the characteristics of high magnetic property, relatively low price, easy processing and the like, is widely applied to a plurality of national pillar industrial fields such as energy, communication, traffic, national defense, medical appliances and the like, and has huge market demand. At present, the sintered neodymium iron boron material is generally prepared by a powder metallurgy method, and the final magnetic property of the sintered neodymium iron boron material is determined by the quality of powder before compression molding to a great extent. The particle size distribution of the powder is a key factor influencing the coercive force and magnetization behavior of the magnet. The two-stage crushing method of hydrogen crushing (HD) and airflow mill superfine crushing is commonly adopted in modern industrial production to prepare powder, the particle size of the powder can be properly adjusted according to requirements, the size distribution is uniform and consistent, and the method is the best method for preparing high-quality sintered magnetic material powder at present. As the last process of the powder preparation method, the powder preparation by the airflow mill becomes one of the key links in the whole material preparation method.

In order to obtain a well-oriented magnetic material, the following requirements are placed on an ideal magnetic powder: the magnetic powder particles are small in size (3-4 microns), the size distribution is narrow, particles of 3-4 microns account for 95%, and particles smaller than 1 micron and larger than 7 microns are avoided, so that all the magnetic powder particles are single crystals. ② the magnetic powder particles are spherical or approximately spherical. ③ the crystal defects of the magnetic powder particles are as few as possible. And fourthly, the magnetic powder particles are preferably crushed along the grain boundary when being crushed, the surface of each particle is rich in neodymium phase as much as possible, and the foundation is laid for preventing the second type of crystal grain boundary from appearing in the liquid phase sintering process. Fifthly, impurities and gas adsorbed on the surfaces of the magnetic powder particles are as less as possible, and especially the oxygen content is less. The five conditions are necessary conditions for preparing the high-quality sintered NdFeB permanent magnet material.

At present, nitrogen sources are generally adopted in the powder preparation of the airflow mill, and the oxidation of material particles can be effectively prevented. However, the coarse powder prepared by the HD method still contains a certain amount of hydrogen although it has been subjected to dehydrogenation treatment, and is liable to react with nitrogen in a specific case, increasing the content of nitrogen in the magnet, and affecting the performance of the permanent magnet material. Meanwhile, the nitrogen has smaller molecular weight and lower kinetic energy transportation efficiency, and the efficiency of crushing coarse powder particles by one-time collision is influenced.

The literature shows that many patents on the preparation of sintered magnetic materials have been directed to improvements in the gas source of the jet mill. The prior art discloses a preparation method of a Re-Fe-B series permanent magnet material containing trace nitrogen, and argon or nitrogen with the temperature not higher than 10 ℃ is suggested to be used as protective gas of a jet mill in the powder preparation process so as to reduce the nitrogen content in the permanent magnet material, but the influence of an argon source on the powder preparation process and final powder is not involved. In the patent of a preparation method of a neodymium iron boron permanent magnet material, nitrogen and argon are mixed to be used as a power carrier of a jet mill, and the probability of one-time collision and crushing among neodymium iron boron particles can be improved by using the mixed gas, but a specific implementation method and actual efficiency are not disclosed. Further, there have been patents disclosing a technique in which hydrogen and helium gases having a smaller molecular weight than nitrogen and argon gas having a larger molecular weight than nitrogen are used as a gas source for gas flow polishing. However, hydrogen and oxygen are explosive gases, helium can reduce the particle size of magnetic powder, but the specific gravity of the ultrafine powder is high, the powder discharging speed is slow, and helium is expensive. In summary, the use of a nitrogen source as the grinding gas in the jet milling process is of practical significance, but the problem to be solved is to overcome a series of adverse effects caused by the nitrogen source.

Disclosure of Invention

In view of the problems in the prior art, the invention provides a method for preparing micro powder of sintered neodymium iron boron permanent magnet material, a target type airflow milling powder used for preparing the micro powder and the obtained airflow milling powder. The invention aims to change the traditional fluidized bed type grinding powder preparation method, adopts target type airflow grinding powder preparation, optimizes the parameters of the airflow grinding method, can better protect micro powder particles, refine the granularity of the micro powder, improve the sphericity of the micro powder particles and improve the particle defects. The sintered Nd-Fe-B permanent magnet material with better coercive force, squareness and magnet performance can be prepared by the micro powder prepared by the method through the subsequent method.

On one hand, the invention discloses micro powder for preparing a sintered neodymium-iron-boron permanent magnet material, wherein the sphericity of the micro powder is more than or equal to 90%, and the particle attachment rate is less than or equal to 10%. Preferably, the sphericity of the micropowder is more than or equal to 94 percent.

Further, the particle size D of the micro powder₅₀2 to 5 μm, and D₉₀/D₁₀2-5. The above-mentionedThe nitrogen content of the micro powder is less than or equal to 300 ppm.

The invention also discloses a target type airflow milling powder preparation method, which can be used for preparing the micro powder.

Wherein: the relationship between the diameter of the target A, the diameter of the side nozzle B, and the distance C between the target and the side nozzle is: and A/B is mx (C/A + B), wherein the value of m ranges from 1 to 7, and preferably ranges from 2 to 5. The speed of the jet air flow of the side nozzle is 320-580 m/s, preferably 400-520 m/s.

The diameter F of the grading wheel and the diameter A of the target center have the following relation: f is p multiplied by A, wherein the value range of p is 3-6, preferably 3.5-4.5.

In a preferred embodiment of the invention, the target, the side nozzle and the grading wheel are all made of silicon nitride.

Preferably, the cyclone separator is used for collecting the micro powder and is provided with holes with the aperture being less than or equal to 1 mu m distributed on the circular flange plate of the baffle plate.

Furthermore, the grinding gas in the target type gas flow powder grinding method is nitrogen, and the grinding pressure is 0.3-0.8 MPa, preferably 0.4-0.7 MPa.

Preferably, the target type jet milling powder process does not produce spitting materials.

The invention also discloses the jet milling powder obtained by the method, and the jet milling powder consists of superfine powder and the micro powder. Wherein the mass of the superfine powder accounts for less than or equal to 0.5 percent of the total mass of the airflow milled powder.

The invention adopts a target type jet mill method to prepare the micro powder of the sintered Nd-Fe-B permanent magnetic material. By optimizing a series of process parameters of the target jet milling process, such as milling pressure, jet air velocity, etc., fine powders having superior properties can be obtained. The invention can reduce the collision frequency of the neodymium iron boron particles in the crushing process by changing the crushing mode of the sheets. The dispersion of the particle size distribution of the micro powder is favorably reduced, and the proportion of the micro powder generated by multiple collisions can be reduced, so that the yield of the qualified micro powder is improved, and the loss of rare earth elements is greatly reduced.

In the invention, the powder discharged in the target type air flow milling process only comprises micro powder and ultra-fine powder, and the content of the ultra-fine powder is very small. The obtained micro powder has uniform particle size distribution, high consistency and narrow range. In addition, no material spitting is generated in the process, and the yield of qualified micro powder is high.

The target type jet milling method has high yield. The obtained qualified micro powder has low nitrogen content and small particle attachment rate, and is suitable for large-scale production of high-quality sintered neodymium iron boron permanent magnet materials.

Drawings

FIG. 1 is a photograph (magnification: 10000) of the microstructure of the fine powder particles of example 1.

Fig. 2 is a photograph (magnification: 10000) of the microstructure of the fine powder particles of comparative example 1.

FIG. 3 is a photograph (magnification: 5000) of the microstructure of the fine powder particles of example 1.

Fig. 4 is a photograph (magnification 5000) of the microstructure of the fine powder particles of comparative example 1.

FIG. 5 is a photograph (magnification 4000) of the microstructure of the fine powder particles of example 1.

Fig. 6 is a microstructure photograph (magnification 4000) of the fine powder particles of comparative example 1.

FIG. 7 is a photograph (magnification 2000) of the microstructure of the fine powder particles of example 1.

Fig. 8 is a photograph (magnification 2000) of the microstructure of the fine powder particles of comparative example 1.

Detailed Description

The following detailed description of the present invention, taken in conjunction with the accompanying drawings and examples, is provided to enable the invention and its various aspects and advantages to be better understood. However, the specific embodiments and examples described below are for illustrative purposes only and are not limiting of the invention.

The preparation of the sintered Nd-Fe-B permanent magnet material comprises two processes of micro powder preparation and sintering, and is specifically realized by the following technical scheme:

and preparing the neodymium iron boron strip sheet with the average thickness of 0.1-0.4 mm by a quick-setting sheet method. The proportion of neodymium, iron, boron and other required elements is not limited, and can be adjusted according to actual needs. Crushing the strip slices into coarse powder by a hydrogen crushing (HD) method, adding a lubricant with the mass ratio of less than or equal to 1% into the coarse powder, and uniformly mixing the coarse powder and the lubricant by a powder mixer. The obtained powder is put into a target type jet mill device, and is further subjected to superfine crushing through the target type jet mill, so that the micro powder required by the sintered neodymium iron boron permanent magnet material can be prepared.

The target jet milling method selects nitrogen as the milling gas, adopts Laval nozzles made of silicon nitride, and has only one side nozzle. In the current fluidized bed type jet milling method, a side nozzle and a bottom nozzle are needed. In the invention, the target center made of silicon nitride is adopted.

Wherein, the diameter A of the target, the diameter B of the side nozzle, and the distance C between the target and the side nozzle satisfy the formula:

A/B＝m×(C/A+B)，

wherein the value range of m is 1-7, preferably 2-5. By controlling the value of m, the dispersion of the particle size distribution of the micro powder can be effectively reduced.

In the method, the speed of the jet air flow of the side nozzle is properly adjusted within the interval of 320-580 m/s, preferably 400-520 m/s. The gas flow in the present invention is a nitrogen gas flow. Under the condition, the micro powder crushing efficiency is high, and the particle size distribution is uniform and consistent.

The grading wheel can be made of silicon nitride, and the diameter F of the grading wheel and the diameter A of the target center meet the formula:

F＝p×A，

wherein the value range of p is 3-6, preferably 3.5-4.5. The method can adjust the gap change in the circumferential direction of the grading wheel, is different from the traditional equidistant distribution, and can ensure the particle size distribution of the micro powder to be narrow.

In the method, the grinding pressure is adjusted to be within the range of 0.3-0.8 MPa in the grinding process, and the grinding pressure is preferably 0.4-0.7 MPa in order to make the particle size distribution of the micro powder better.

In the micro powder collecting procedure, a special baffle is arranged at the outlet of the cyclone separator, and small holes with the aperture being less than or equal to 1 mu m are densely distributed on a circular flange of the baffle, so that only nitrogen and a small amount of micro powder are allowed to pass through.

In the invention, the final powder output of the target type airflow milling powder method only comprises two parts of qualified micro powder and ultra-fine powder, and no material spitting exists. Wherein the mass of the superfine powder accounts for less than or equal to 0.5 percent of the total mass of the powder. In addition, in the invention, the final powder output only comprises qualified micro powder and ultra-fine powder, namely the mass of the ultra-fine powder accounts for less than or equal to 0.5 percent of the total mass of the input powder.

In the traditional fluidized bed type air flow milling method, a certain amount of spitting materials always remain in a milling cavity, the efficiency in the final milling process is low, and the particle size, the density and the components of micro powder are not uniform, so that the micro powder can be used only through the subsequent powder mixing process. The target type jet milling method of the invention has no material discharge completely, and the powder granularity is uniform in the whole milling stage.

In the method, by controlling the numerical values of m and p and the jet air flow velocity of the side nozzle, the more ideal micro powder for preparing the sintered neodymium iron boron permanent magnet material can be obtained.

The nitrogen content of the micro powder obtained by the invention is less than or equal to 300 ppm. The sphericity of the micro powder is more than 90 percent, and the particle attachment rate is less than or equal to 10 percent. And the particle size D of the fine powder₅₀In the range of 2 to 5 μm, D₉₀/D₁₀The ratio is 2-5, namely the size distribution of the micro powder particle size is narrow.

In the present invention, the sphericity of the micropowder is defined as: in the microstructure picture, the micro-powder particles with the length-width ratio close to 1:1 are spherical micro-powder particles, and the proportion of the spherical micro-powder particles in the total number of the micro-powder particles is counted to obtain the sphericity of the micro-powder.

In the present invention, the particle adhesion ratio is defined as: in the microstructure photo, 3 or more than 3 small particles with the particle size less than 1 μm are attached to the surface of the micro powder particles, and the micro powder is the non-attached particles, the difference between the total number of the micro powder particles and the number of the micro powder of the non-attached particles is counted, and the ratio of the difference to the total number of the micro powder particles is the particle attachment rate.

Adding antioxidant with the mass ratio of less than or equal to 1% into the micro powder, uniformly mixing, and pressing and molding in a magnetic field with the mass ratio of more than 1.4T to prepare a green body. And putting the green body into a vacuum furnace, and sintering at the temperature of 1000-1100 ℃. And then performing two-stage tempering treatment on the sintered billet within the temperature ranges of 860-930 ℃ and 450-550 ℃ respectively to finally obtain the sintered neodymium iron boron blank magnet.

Example 1

The neodymium iron boron alloy ingot is prepared into a strip sheet with the average thickness of 0.32mm by adopting a rapid hardening sheet method, and the composition of the strip sheet is Nd₃₁Dy₁Co₁Cu_0.1Zr_0.08Ga_0.12Al_0.1Nb_0.3Fe_balB_0.97(wt.%, in mass percent). Crushing the neodymium iron boron quick-setting thin strip pieces by an HD method to obtain coarse powder. 0.05 wt% of lubricant is added into the coarse powder and mixed evenly by a powder mixer. And carrying out superfine crushing on the uniformly mixed powder by a target type jet mill. The grinding pressure is 0.6MPa, the jet mill nozzle and the target material are both silicon nitride Laval nozzles, m in the formula of the diameter of the target center, the diameter of the side nozzle and the distance between the target center and the side nozzle is 3, and the jet air velocity is 400 m/s. Meanwhile, a ceramic grading wheel is selected, and in the formula of the diameter of the ceramic grading wheel and the diameter of the target center, p is 4. The final powder output is divided into two parts, the qualified micro powder accounts for about 99.5 percent of the total weight of the input powder, the proportion of the ultra-fine powder is 0.5 percent, and no material is discharged in a grinding chamber. Adding 0.1 wt% of antioxidant into the micro powder, and mixing uniformly by a powder mixer. And pressing and molding the uniformly mixed micro powder in a vertical magnetic field press with the temperature of more than 1.4T. And putting the pressed compact into a vacuum sintering furnace, sintering for 4 hours at 1050 ℃, and performing two-stage tempering heat treatment at 920 ℃ for 2 hours and 480 ℃ for 3 hours to obtain the sintered neodymium iron boron blank magnet.

Comparative example 1

The same strip pieces as in example 1 were prepared, and after being crushed into coarse powder by the HD method, they were subjected to ultrafine crushing by a jet mill. Wherein, the jet mill adopts a conventional fluidized bed type jet mill method, and the rest pressing type sintering parameters are the same as those of the embodiment 1. Table 1 shows the performance parameters, powder performance indexes and final magnet magnetic performance of the sintered nd-fe-b permanent magnet material prepared in example 1 and comparative example 1.

TABLE 1 comparison of preparation Processes, micropowder Properties and magnetic Properties of magnet in example 1 and comparative example 1

As can be seen from table 1, the yield of the qualified fine powder of the sintered ndfeb permanent magnet material prepared in example 1 is higher than that of comparative example 1. Meanwhile, the nitrogen content of the micro powder is low, the particle size distribution range is narrow, and the coercivity and the squareness of the finally prepared magnet are higher. Therefore, the method for preparing powder by target-type airflow milling in the embodiment 1 can not only improve the yield of qualified micro powder in the powder, but also prepare the sintered Nd-Fe-B permanent magnet material with higher coercivity and squareness by using the micro powder.

Meanwhile, the micro powder produced after the target type jet mill and the fluidized bed type jet mill are compared. From the micrographs at different magnifications shown in FIGS. 1 to 8, 500 fine powder particles were counted. Statistical results show that in example 1, the sphericity of the micropowder is about 98.5%, and the proportion of micropowder with no small particles attached is about 92.5%; in comparative example 1, the sphericity of the fine powder was about 80.3%, and the proportion of the fine powder having no small particles adhered thereto was about 70.9%.

Example 2

The neodymium iron boron alloy ingot is prepared into a strip sheet with the average thickness of 0.1mm by adopting a rapid hardening sheet method, and the composition of the strip sheet is (PrNd)_30.8Co_0.5Cu_0.06Zr_0.10Ga_0.10Al_0.3Nb_0.3Fe_balB_0.94(wt.%, in mass percent). Crushing the neodymium iron boron quick-setting thin strip pieces by an HD method to obtain coarse powder. 0.5 wt% of lubricant is added to the coarse powder and mixed by a powder mixer. And carrying out superfine crushing on the uniformly mixed powder by a target type jet mill. The grinding pressure is 0.3MPa, the jet mill nozzle and the target material are both silicon nitride Laval nozzles, m in the formula of the diameter of the target center, the diameter of the side nozzle and the distance between the target center and the side nozzle is 2, and the jet air flow speed is 520 m/s. Meanwhile, a ceramic grading wheel is selected, and in the formula of the diameter of the ceramic grading wheel and the diameter of the target center, p is 3.5. The final powder output is divided into two parts, the qualified micro powder accounts for about 99.7 percent of the total weight of the input powder, the proportion of the ultra-fine powder is 0.3 percent, and no material is discharged in a grinding chamber. Adding 0.3 wt% of antioxidant into the micro powder, and mixing uniformly by a powder mixer. Vertical magnetism of the mixed micro powder at more than 1.4TAnd pressing and forming in a field press. And putting the pressed blank into a vacuum sintering furnace, sintering for 4 hours at 1040 ℃, and performing two-stage tempering heat treatment at 890 ℃ for 2 hours and 490 ℃ for 3 hours to obtain the sintered neodymium iron boron blank magnet.

Comparative example 2

The same strip pieces as in example 2 were prepared, and after being crushed into coarse powder by the HD method, they were subjected to ultrafine crushing by a jet mill. Wherein, the jet mill adopts a conventional fluidized bed type jet mill method, and the rest pressing type sintering parameters are the same as those of the embodiment 2. Table 2 shows the performance parameters, powder performance indexes, and final magnet magnetic properties of the processes for preparing the ndfeb permanent magnet materials according to example 2 and comparative example 2.

TABLE 2 comparison of the preparation Processes, micropowder Properties and magnetic Properties of magnets of example 2 and comparative example 2

As can be seen from table 2, the yield of the qualified fine powder of the sintered ndfeb permanent magnet material prepared in example 2 is higher than that of comparative example 2. Meanwhile, the nitrogen content of the micro powder is low, the particle size distribution range is narrow, and the coercivity and the squareness of the finally prepared magnet are higher. Therefore, the method for preparing powder by target-type airflow milling in the embodiment 2 can not only improve the yield of qualified micro powder in the powder, but also prepare the sintered Nd-Fe-B permanent magnet material with higher coercivity and squareness by using the micro powder.

Meanwhile, the micro powder produced after the target type jet mill and the fluidized bed type jet mill are compared. 500 micro powder particles were counted using the microstructure photograph. Statistics show that the sphericity of the fine powder in example 2 is about 96.0%, and the proportion of the fine powder having no small particles adhered thereto is about 91.6%. In comparative example 2, the sphericity of the fine powder was about 82.5%, and the proportion of the fine powder having no small particles attached thereto was about 73.4%.

Example 3

The neodymium iron boron alloy ingot is prepared into a strip sheet with the average thickness of 0.4mm by adopting a rapid hardening sheet method, and the composition of the strip sheet is (PrNd)₂₆Dy₅Co_1.3Cu_0.15Zr_0.08Ga_0.16Al_0.25Fe_balB_0.97(wt.%, in mass percent). Crushing the neodymium iron boron quick-setting thin strip pieces by an HD method to obtain coarse powder. 0.3 wt% of lubricant is added to the coarse powder and mixed by a powder mixer. And carrying out superfine crushing on the uniformly mixed powder by a target type jet mill. The grinding pressure is 0.8MPa, the jet mill nozzle and the target material are both silicon nitride Laval nozzles, m in the formula of the diameter of the target center, the diameter of the side nozzle and the distance between the target center and the side nozzle is 5, and the jet air flow speed is 320 m/s. Meanwhile, a ceramic grading wheel is selected, and in the formula of the diameter of the ceramic grading wheel and the diameter of the target center, p is 4.5. The final powder output is divided into two parts, the qualified micro powder accounts for about 99.6 percent of the total weight of the input powder, the proportion of the ultra-fine powder is 0.4 percent, and no material is discharged in a grinding chamber. Adding 0.3 wt% of antioxidant into the micro powder, and mixing uniformly by a powder mixer. And pressing and molding the uniformly mixed micro powder in a vertical magnetic field press with the temperature of more than 1.4T. And putting the pressed compact into a vacuum sintering furnace, sintering for 4 hours at 1065 ℃, and performing two-stage tempering heat treatment at 920 ℃ for 2 hours and 480 ℃ for 6 hours to obtain the sintered neodymium-iron-boron blank magnet.

Comparative example 3

The same strip pieces as in example 3 were prepared, and after being crushed into coarse powder by the HD method, they were subjected to ultrafine crushing by a jet mill. Wherein, the jet mill adopts a conventional fluidized bed type jet mill method, and the rest pressing type sintering parameters are the same as those of the embodiment 3. Table 3 shows the performance parameters, powder performance indexes and final magnet magnetic performance of the processes for preparing the ndfeb permanent magnet materials according to example 3 and comparative example 3.

Table 3 comparison of the production process, micropowder Properties and magnetic Properties of magnet in example 3 and comparative example 3

As can be seen from table 3, the yield of the qualified fine powder of the sintered ndfeb permanent magnet material prepared in example 3 is higher than that of comparative example 3. Meanwhile, the nitrogen content of the micro powder is low, the particle size distribution range is narrow, and the coercivity and the squareness of the finally prepared magnet are higher. Therefore, the method for preparing powder by target-type airflow milling in the embodiment 3 can not only improve the yield of qualified micro powder in the powder, but also prepare the sintered Nd-Fe-B permanent magnet material with higher coercivity and squareness by using the micro powder.

Meanwhile, the micro powder produced after the target type jet mill and the fluidized bed type jet mill are compared. 500 micro powder particles were counted using the microstructure photograph. Statistics show that in example 3, the sphericity of the fine powder was about 97.2%, and the proportion of the fine powder having no small particles adhered thereto was about 93.5%. In comparative example 3, the sphericity of the fine powder was about 87.4%, and the proportion of the fine powder having no small particles adhered thereto was about 76.8%.

Example 4

The neodymium iron boron alloy ingot is prepared into a strip sheet with the average thickness of 0.15mm by adopting a rapid hardening sheet method, and the composition of the strip sheet is Nd₃₁Dy₁Co₁Cu_0.1Zr_0.08Ga_0.12Al_0.1Nb_0.3Fe_balB_0.97(wt.%, in mass percent). Crushing the neodymium iron boron quick-setting thin strip pieces by an HD method to obtain coarse powder. 0.05 wt% of lubricant is added into the coarse powder and mixed evenly by a powder mixer. And carrying out superfine crushing on the uniformly mixed powder by a target type jet mill. The grinding pressure is 0.4MPa, the jet mill nozzle and the target material are both silicon nitride Laval nozzles, m in the formula of the diameter of the target center, the diameter of the side nozzle and the distance between the target center and the side nozzle is 1, and the jet air velocity is 580 m/s. Meanwhile, a ceramic grading wheel is selected, and in the formula of the diameter of the ceramic grading wheel and the diameter of the target center, p is 3. The final powder output is divided into two parts, the qualified micro powder accounts for about 99.5 percent of the total weight of the input powder, the proportion of the ultra-fine powder is 0.5 percent, and no material is discharged in a grinding chamber. Adding 0.3 wt% of antioxidant into the micro powder, and mixing uniformly by a powder mixer. And pressing and molding the uniformly mixed micro powder in a vertical magnetic field press with the temperature of more than 1.4T. And putting the pressed compact into a vacuum sintering furnace, sintering for 4 hours at 1050 ℃, and performing two-stage tempering heat treatment at 920 ℃ for 2 hours and 480 ℃ for 3 hours to obtain the sintered neodymium iron boron blank magnet.

Comparative example 4

The same strip pieces as in example 4 were prepared, and after being crushed into coarse powder by the HD method, they were subjected to ultrafine crushing by a jet mill. Wherein, the jet mill adopts a conventional fluidized bed type jet mill method, and the rest pressing type sintering parameters are the same as those of the embodiment 4. Table 4 shows the performance parameters, powder performance indexes and final magnet magnetic performance of the sintered nd-fe-b permanent magnet materials prepared in example 4 and comparative example 4.

Table 4 comparison of the production process, micropowder Properties and magnetic Properties of magnet in example 4 and comparative example 4

As can be seen from table 4, the yield of the qualified fine powder of the sintered ndfeb permanent magnet material prepared in example 4 is higher than that of comparative example 4. Meanwhile, the nitrogen content of the micro powder is low, the particle size distribution range is narrow, and the coercivity and the squareness of the finally prepared magnet are higher. Therefore, the method for preparing powder by target-type airflow milling in the embodiment 4 can not only improve the yield of qualified micro powder in the powder, but also prepare the sintered Nd-Fe-B permanent magnet material with higher coercivity and squareness by using the micro powder.

Meanwhile, the micro powder produced after the target type jet mill and the fluidized bed type jet mill are compared. 500 micro powder particles were counted using the microstructure photograph. Statistics show that in example 4, the sphericity of the fine powder is about 96.2%, and the proportion of the fine powder having no small particles attached thereto is about 90.8%. In comparative example 4, the sphericity of the fine powder was about 80.3%, and the proportion of the fine powder having no small particles adhered thereto was about 70.9%.

Example 5

The neodymium iron boron alloy ingot is prepared into a strip sheet with the average thickness of 0.20mm by adopting a rapid hardening sheet method, and the composition of the strip sheet is Nd₃₁Dy₁Co₁Cu_0.1Zr_0.08Ga_0.12Al_0.1Nb_0.3Fe_balB_0.97(wt.%, in mass percent). Crushing the neodymium iron boron quick-setting thin strip pieces by an HD method to obtain coarse powder. 0.05 wt% of lubricant is added into the coarse powder and mixed evenly by a powder mixer. And carrying out superfine crushing on the uniformly mixed powder by a target type jet mill. The grinding pressure is 0.7MPa, the jet mill nozzle and the target material are silicon nitride Laval nozzles, the diameter of the target center, the diameter of the side nozzle, the target center and the side nozzleThe distance between the two air jets is 1, and the jet air flow speed is 450 m/s. Meanwhile, a ceramic grading wheel is selected, and in the formula of the diameter of the ceramic grading wheel and the diameter of the target center, p is 6. The final powder output is divided into two parts, the qualified micro powder accounts for about 99.5 percent of the total weight of the input powder, the proportion of the ultra-fine powder is 0.5 percent, and no material is discharged in a grinding chamber. Adding 0.3 wt% of antioxidant into the micro powder, and mixing uniformly by a powder mixer. And pressing and molding the uniformly mixed micro powder in a vertical magnetic field press with the temperature of more than 1.4T. And putting the pressed compact into a vacuum sintering furnace, sintering for 4 hours at 1050 ℃, and performing two-stage tempering heat treatment at 920 ℃ for 2 hours and 480 ℃ for 3 hours to obtain the sintered neodymium iron boron blank magnet.

Comparative example 5

The same strip pieces as in example 5 were prepared, and after being crushed into coarse powder by the HD method, they were subjected to ultrafine crushing by a jet mill. Wherein, the jet mill adopts a conventional fluidized bed type jet mill method, and the rest pressing type sintering parameters are the same as those of the embodiment 5. Table 5 shows the performance parameters, powder performance indexes and final magnet magnetic performance of the sintered nd-fe-b permanent magnet materials prepared in example 5 and comparative example 5.

TABLE 5 comparison of preparation Processes, micropowder Properties and magnetic Properties of magnet in example 5 and comparative example 5

As can be seen from table 5, the yield of the qualified fine powder of the sintered ndfeb permanent magnet material prepared in example 5 is higher than that of comparative example 5. Meanwhile, the nitrogen content of the micro powder is low, the particle size distribution range is narrow, and the coercivity and the squareness of the finally prepared magnet are higher. Therefore, the method for preparing powder by using the target type airflow milling in the embodiment 5 not only can improve the yield of qualified micro powder in the powder, but also can prepare the sintered neodymium iron boron permanent magnet material with higher coercivity and squareness by using the micro powder.

Meanwhile, the micro powder produced after the target type jet mill and the fluidized bed type jet mill are compared. 500 micro powder particles were counted using the microstructure photograph. Statistical results showed that in example 5, the sphericity of the fine powder was about 94.3%, and the proportion of the fine powder having no small particles adhered thereto was about 91.6%. In comparative example 5, the sphericity of the fine powder was about 80.3%, and the proportion of the fine powder having no small particles adhered thereto was about 70.9%.

According to the comparison result between the embodiment adopting the target type jet mill and the comparative example adopting the fluidized bed type jet mill, the micro powder of the sintered neodymium iron boron permanent magnet material prepared by the invention has higher sphericity and smaller probability of small particles attached to the surface of the micro powder. The nitrogen content of the micro powder particles is lower, the particles are uniformly distributed, and the size range is narrow. And the method has no spitting material in the powder discharging process. The sintered Nd-Fe-B permanent magnet material prepared by the micro powder has higher coercive force and squareness.

Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims

1. The micro powder for preparing the sintered neodymium-iron-boron permanent magnet material is characterized in that the sphericity of the micro powder is more than or equal to 90%, the particle attachment rate is less than or equal to 10%, and the nitrogen content of the micro powder is less than or equal to 300 ppm;

wherein, the sphericity of the micro powder is as follows: in the microstructure picture, the particles with the length-width ratio close to 1:1 are spherical micro powder particles, and the proportion of the spherical micro powder particles in the total number of the micro powder particles is counted to obtain the sphericity of the micro powder;

the particle attachment ratio is: in the microstructure picture, 3 or more than 3 small particles with the particle size less than 1um are attached to the surfaces of the micro powder particles and are micro powder of non-attached particles, the difference between the total number of the micro powder particles and the number of the micro powder of the non-attached particles is counted, and the ratio of the difference to the total number of the micro powder particles is the particle attachment rate;

particle size D of the micropowder₅₀2 to 5 μm, and D₉₀/ D₁₀=2～5。

2. A targeted jet milling process for producing the micropowder of claim 1, wherein:

the relationship between the diameter of the target A, the diameter of the side nozzle B, and the distance C between the target and the side nozzle is: A/B = mx (C/A + B), wherein m ranges from 1 to 7; the speed of the jet air flow of the side nozzle is 320-580 m/s;

the diameter F of the grading wheel and the diameter A of the target center have the following relation: f = p × A, wherein p ranges from 3 to 6.

3. The method as claimed in claim 2, wherein a cyclone is used to collect the micropowder and is arranged such that holes having a pore size of less than or equal to 1 μm are distributed in the circular flange of the baffle.

4. The method according to claim 2, wherein m is in a range of 2 to 5.

5. The method according to claim 2, wherein the velocity of the side nozzle jet air flow is 400 to 520 m/s.

6. The method according to claim 2, wherein p has a value in the range of 3.5 to 4.5.

7. The method of claim 2, wherein the bulls-eye, side nozzle, and classifier wheel are made of silicon nitride.

8. The method according to claim 2, wherein the grinding gas is nitrogen, and the grinding pressure is 0.3 to 0.8 MPa.

9. The method of claim 8, wherein the grinding pressure is 0.4 to 0.7 MPa.

10. The method of claim 2, wherein the targeted jet milling process does not produce spitting.

11. An air-milled powder obtained by the method according to any one of claims 2 to 10, wherein the mass ratio of the fine powder to the total mass of the air-milled powder is not less than 99.5%.